Pressure vessel of the boiler type and method of producing same



May 30, 1939. a. M. TREFTS, 3D ,3

-PRESSURE VESSEL OF THE BOILER TYPE AND METHOD OF PRODUCING SAME Filed Nov. 16, 1936 2 Sheets-Sheet 1 OOOOL 4; 00006 oon INVENTO v 000000000000 $1 6 OLD TTO NEYS May 30, 1939. G. M. TREFTS, 3D

PRESSURE VESSEL OF THE BOILER TYPE AND METHOD OF PRODUCING SAME I Filed Nov. 16, 1936 2 Sheets-Sheet 2 George? QM ATTO :ZEYS

Patented May 30, 1939 UNITED STATES PATENT OFFECE PRESSURE VESSEL OF THE BOILER TYPEv AND METHOD OF PRODUCING SAME 8 Claims.

This invention relates to steam generators and pressure vessels, and pertains more especially to certain improvements in the manufacture of boilers having their shell plates and head or other 5 closure members secured together by Welding.

One object of the invention is to design a vessel so that the welded girth joints, as for example, between the main boiler shell and heads, and between the firebox shell and heads, lie in the 10. planes of the heads, inside of the perimetral outlines of the adjoining shell members.

Another object is to design a vessel in the manner aforesaid whereby the welding process, when forming the joints between the shell plates and the head members or closure members, may be accomplished under ideal conditions, continuously and without interruption, and in a particular manner as will be fully explained hereinafter.

20 Another object of the invention is to design a boiler in the manner aforesaid, whereby the head plates or shell closure members of the boiler and/or the firebox are of reduced dimension relative to the sectional areas of the adjacent 25 shell portions of the boiler or firebox respectively,

and are subjected to lower total internal longitudinal pressures when in service, as compared to previous forms of boiler head construction, whereby lower unit stresses are transmitted to'the welded joints.

In the accompanying drawings:

Fig. 1 is a longitudinal sectional view of a locomotive type boiler illustrating the invention;

Fig. 2 is an elevation of the firebox end of the boiler shown in Fig. I with a portion of the back boiler head broken away to reveal parts of the internal boiler and firebox construction;

Fig. 3 is a detached perspective View of the firebox under process of formation, showing weld- 40 ing apparatus in position for operation thereon;

Fig. 4 is an end view of a cylindrical shell boiler, showing an end plate welded in position in accordance with the invention.

It has been the common practice heretofore 45 in connection with welded joint constructions for boilers and other pressure vessels to form the various head or other closure members with integral turned flanges about their perimetral margins for butting contact with the end edges 50 of the casing or shell element thereof preparatory to application of the welding process. For example, the shell plates were rolled up from suitably cut blanks to form the shell of cylindrical or box-shape form as the case demanded, with 55 straight edges; and the head plates were pressed or forged into shape with marginal edge turned flanges to meet the edges of the shell members. To assemble these parts through use of the welding process, a shell member was first trued up to its ultimate shape, and then while being sup- 5 ported with its longitudinal axis in a substantially horizontal position the head plate was moved into position adjacent the end of the shell with the head plate flange meeting the marginal edge of the shell in butting relation. The parts were then temporarily supported in this position, and the welding process commenced.

Because the molten metal during the welding process naturally flows downwardly as a result of the force of gravity, only that portion of the joint which resides in the uppermost horizontal plane is properly presented for welding. It is a commonly accepted fact that conditions most suitable for a satisfactory or perfect weld are present only when the line of weld lies in a substantially horizontal plane, to which access may be had by the operator of the welding equipment from above, as distinguished from below or from the side. Only from such position may the molten metal follow a natural path toward a complete filling of the joint at the exact point of application of the welding heat.

Therefore, in connection with previous methods it was necessary to frequently shift the shell and the accompanying head plate about the longitudinal axis of the shell so that the immediate portion of the line of joint being welded at any one time would be presented to the welding operator in a substantially horizontal plane, accessible from above. This meant that the proc- 5 ess of welding the girth seams was necessarily interrupted a large number of times during'the welding of each seam, and this detracted greatly from the efiiciency of the process and the uniformity of the completed weld. This was par- 40 ticularly true in the case of cylindrical shell constructions wherein the curvature of the shell made it extremely difiicult to provide suitable conditions for welding the girth seams.

By my invention the casing or shell elements and head or other closure members therefor are so constructed that each line of joint therebetween or integral portion thereof lies in a single plane that may be disposed horizontally during the welding process. This arrangement permits each integral portion of the joint to be presented in a single horizontal plane which may be approached by the welder from above without shifting the attitude of the parts, and thus, a continuous uniformly welded seam may be produced 5 without interruption from start to finish and without the use of complicated and otherwise unsatisfactory work rotating apparatus. The invention is exemplified by the forming of a shell or casing element from metal plates into open end tubular or other closed body form having a marginal edge portion of the casing sheet bent into the plane of the open end or wall member therefor, the term end wall being used generically to include any angularly related wall portion of the boiler casing structure. Thus, the turned marginal edge portion of the casing sheet constitutes a substantial portion of the end wall of the casing member and provides a one piece casing structure with an opening in an end wall portion thereof. A closure element for the end wall opening is provided with marginal edge portions adapted to register with the marginal edge portions of the turned flange of the casing sheet and to provide therebetween a line of joint that is disposed in a single plane. Preparatory to the process of welding this line of joint the parts are supported in proper relative position by some temporary connecting means and the whole is shifted to an attitude wherein the joint is in a horizontal plane and presented upwardly for convenient approach from above by the welding apparatus.

In the present instance, referring to Figures 1, 2 and 3, I have shown a locomotive type boiler comprising a fire box casing l, a barrel or boiler shell 2, a back boiler head 3, a fire box side wall 4', a crown sheet 5, a back firebox head 6, a rear tube sheet 1, a mud ring 8, and the usual staybolts 9. The casing l is provided at its back end with an inturned flange H, and the back boiler head 3 which is in the form of a fiat sheet is welded to the marginal edges of the flange on the line a. The firebox shell, comprising a pair of side walls 4 and a crown sheet 5, is formed at both ends with inturned flanges l2, and is welded to the head 6 and the tube sheet I on the lines 11 and 0 respectively.

Figure 3 illustrates the rectangular style of fire box wherein the shell has been formed with in-turned flanges l2 at each end. The rear tube sheet I is shown already welded in position, and the welding of the rear fire box head 6 to the fire box shell is in process. Figure 4 illustrates the application of the invention to a cylindrical shaped boiler shell, wherein l5 designates a circular head plate or other closure member which has been welded along line d to the flange Ii which is integral with the shell.

In accordance with my invention I first form a blank from metal plate for the shell or casing element of the boiler portion to be constructed, and preferably while it is in flat condition I form integral laterally extending flanges thereon by turning the marginal edge portions thereof by rolling, pressing, or some other suitable method. The plate may then be bent into its ultimate general contour, but it is contemplated, however, that the casing or shell blank may first be bent into its general contour, and the integral flanges thereof subsequently. turned by some suitable method. The heads or end plates or other 010- sure or partial closure members for the casing element are then formed or fabricated into the desired shapes therefor and may be either in the form of simple fiat plates of uniform or varying thicknesses or in the form of fabricated elements such as fireboxes or the like which are inserted in the openings provided upon formation of the shell or casing element and thereby constitute closures therefor. The marginal edge portions of these closure elements are formed so as to be adapted to fit into the openings provided between opposed flange portions of the casing or shell element and to register with corresponding marginal edge portions of the flanges for welding thereto to complete the boiler casing structure. The parts are then held by some suitable temporary means in proper relative position and the whole is supported successively in such attitudes as are required to ultimately dispose each portion of the joint between the parts in a substantially horizontal plane and in such manner as to make the joint available for approach by the welding apparatus from above the plane thereof so that each line of weld may be completed in one uninterrupted welding operation, as described hereinabove.

For example, the construction illustrated in Figs. 1, 2 and 4 is provided by forming the inturned integral flange ll of the marginal edge portion of the casing l and inserting the head plate 3 within the opening between opposed marginal edge portions of the flange H. The head 3 is so dimensioned as to provide for a butt joint between the marginal edge portions of the flange l! and the head 3. The parts are then held in proper relative position by some temporary supporting means such as clamps or the like and the casing is then stood upon its end opposite to the head 3, thus disposing the line of the joint between the flange H and the head 3 in a horizontal plane. The welding apparatus is then brought into operation from above the line of the joint, and as explained hereinabove, the welding process may then be performed under ideal conditions from the standpoint of the weld being produced. Inasmuch as the welding of the entire length of the line of joint between the head 3 and the casing I may be completed in one uninterrupted operation, and because the welding metal is enabled to flow directly downwardly into the crevice between the marginal edge portions of the flange and of the closure, there is no tendency toward the production of a line of weld that is made up of sections imperfectly merged one into another, as is the case whenever the welding of a line of joint is intermittently proceeded with. Braces H in the form of stay rods connected at their opposite ends to and extending between marginal edge portions of the casing l and the head 3 (Fig. 1), are provided to span the line of weld 11, thus bracing the structure adjacent the line of weld and relieving the weld of stresses that would otherwise be produced therein by bending moments set up by operating pressure forces against the casing and head plates.

As illustrated in Fig. 3, the firebox of a boiler of the locomotive type may also be fabricated in the manner of the process described hereinabove which relates to the connection of any boiler casing or shell element and end plates or other closure elements therefor, and it will be apparent that any other type or shape of closure member for a casing element may be connected thereto in a similar manner. For instance the fire box per se may be welded into connection with the boiler casing structure in the same manner, as the firebox constitutes a closure for the casing and may be welded thereto by operation of the welding apparatus from above when the parts are disposed in upside down position. In such case the firebox is provided with marginal edge portions turned into the plane of and disposed in registering relation with corresponding adjacent inturned integral flanges formed on the boiler casing or head members. The parts are then supported in proper relative position and in such an attitude that the lines of joint between the firebox and the shell or casing structure are in horizontal planes susceptible of approach from above by the welding apparatus for ideal welding conditions. The welding processesv could then be performed in accordance with the principles of the invention without interruption. As shown in Fig. 1, short stay bolts 9 are arranged between opposed portions of the firebox plates and the casing or wrapper sheets adjacent the points of connection therebetween in such manner as to span the joints and to provide bracing effects similar to those described hereinabove in connection with the bracing members ll. It will be apparent that the features of this welded construction method may be employed as described hereinabove in connection with the fabrication of boiler casing and firebox constructions either in toto or in combination with riveted lapped joint or other conventional types of construction methods. That is, if desired, some portions of the firebox flange may be connected to the corresponding registering portions of the casing flange by the welding process described and other portions thereof may be joined together by riveted lapped joint construction, or the like. Thus it is clearly shown how the welding process is conducted under ideal conditions and how the quality of the welded seam so produced may be uniformly high, and how the labor and expense of handling the parts is materially reduced.

It is also apparent how this design for boiler construction strengthens the longitudinal walls of the boiler shell and firebox by reason of the removal of the girth seams therefrom. At the same time it also results in a reduced unit stress being transmitted to the seam weld by reason of the reduction in area of the end plates inside of the weld, whereby a reduced total internal longitudinal pressure is exerted against the head members when the boiler is in service.

It will be understood that the principles of the invention are applicable with equal facility to either the so-called single or double V butt weld types of welding methods. Throughout this specification the terms casing and shell are used to refer to any hollow body portion of a boiler or pressure vessel construction such as a boiler barrel of a locomotive type boiler; a boiler shell as of the horizontal return tubular, or Scotch marine, or vertical tubular boiler types; the firebox wrapper sheet and firebox casing assembly consisting of the firebox wrapper sheet, the casing head and the throat sheet assembly of boilers of the locomotive and firebox types; shell or wrapper portions of firebox structures; and in connection with the production of any hollow or semi-hollow cylindrical, box, or drum-like portion of any pressure vessel or boiler.

It will be understood that this invention can be used in connection with any type of boiler or pressure vessel, and the scope of the invention is not to be considered as limited to the details of construction shown herein.

I claim:

1. The method of constructing parts of a pressure vessel of the boiler type consisting in forming an open end chambered casing portion from metal plate, the marginal edge portions of said casing being bent at right angles adjacent said opening to form portions of a closure for said opening, inserting a closure member within the opening defined by opposed marginal edge portions of said angularly bent casing portions, said closure member having marginal edgev portions registering with and substantially equal in thickness to the corresponding marginal edge portions of said angularly bent casing portions at the zones of registry therewith, and connecting the marginal edges of said closure members and said casing member by a system of butt welding, the welding operation being performed from above the lines of the joints and while disposed in substantially horizontal attitude.

2. The method of constructing parts of a pressure vessel of the boiler type consisting in forming an open end chambered casing-portion from metalplate with angularly bent marginal edge portions of said casing adjacent said opening forming portions of a closure for said opening, in serting a closure member Within the opening delined by opposed marginal edge portions of said angularly bent casing portions, said closure member having marginal edge portions registering with and substantially equal in thickness to the corresponding marginal edge portions of said angularly bent casing portions at the zones of registry therewith, and connecting the marginal edges of said closure members and said casing member by a system of butt welding, the welding operation being performed from above the lines of the joints and while disposed in substantially horizontal attitude, and relatively bracing the marginal edge portions joined by said system of welding by means of stay elements extending between and connected at their opposite ends to said casing and said closure member adjacent said marginal edge portions and spanning said system of welding to relieve the latter from operating pressure bending moment forces therein.

3. A pressure vessel of the boiler type comprising a casing element formed by bending metal plate and having an integral marginal flange of substantial width at one end thereof turned into a position disposed substantially normal to the axis of said casing, and a substantially fiat end plate having marginal edge portions of substantially uniform thickness constituting a closure for the opening between opposed portions of said marginal flange and secured thereto by welding from above with the joint therebetween disposed in a substantially horizontal position to join opposite side portions of the casing by an end wall in which the marginal portion of the latter which comprises the flange constitutes an integrally connected continuation of theside portions of the casing whereby the weld constitutes the sole means for locally securing the marginal edge portions of said plate to said flange and is protected by the flange against radially directed operating pressure forces.

4. A casing for pressure vesssels of the boiler type including an open end shell portion having an integral marginal flange of substantial width at an open end thereof bent inwardly to a posi- I posite side portions of said shell by an end wall in which the marginal portion of the latter which comprises the flange constitutes an integrally connected continuation of the side portions of the shell, whereby the weld constitutes locally the sole means for relatively securing the marginal edge portions of said closure member and said shell and is protected by the flange against radially directed operating pressure forces.

5. A pressure vessel of the boiler type, including a casing element having an integral marginal flange of substantial width at one end thereof bent inwardly to a position substantially normal to the axis of said casing, and a substantially flat closure member for the opening between opposed portions of said marginal flange, the marginal edges of said marginal flange and said closure member immediately adjacent the line of joint therebetween being of substantially equal thicknesses and secured together by welding from above with the joint therebetween disposed in a substantially horizontal position to join opposite side portions of the casing by an end wall in which the marginal portion of the latter which comprises the flange constitutes an integrally connected continuation of the side portions of the shell, whereby the weld constitutes the sole means for locally securing the marginal edge portions of said plate to said flange and is protected by the flange against radially directed operating pressure forces.

6. A casing for pressure vessels of the boiler type including an open end shell portion having an integral marginal flange of substantial width at an open end thereof bent inwardly to a position substantially normal thereto and providing a marginal wall portion for said end, a closure member disposed within the opening defined by the marginal edge portions of said flange and having marginal edge portions in registry therewith and substantially equal in thickness at the zones of registry therewith to corresponding adjacent marginal edge portions of said flange and secured thereto by a system of butt welding from above with the line of the joint therebetween disposed in a substantially horizontal position to join opposite side portions of said shell by an end wall in which the marginal portion of the latter which comprises the flange constitutes an integrally connected continuation of the side portions of the shell, and stay elements extending between and connected at their opposite ends to said casing and said closure member adjacent said system of welding and spanning the latter, whereby the weld constitutes locally the sole means for relatively securing the marginal edge portions of said closure member and said shell and is protected by the flange against radially directed operating pressure forces imposed upon said shell portion, and against bending moments therein by said stay elements.

7. A boiler shell shaped from metal plate having a marginal portion thereof bent inwardly to form a portion of an end wall of said shell whereby to provide a one piece casing with an opening in an end wall thereof, a closure member for said opening having marginal edge portions in registry with the marginal edge portions of said inwardly turned marginal portion of said shell and secured thereto by a system of welding from above with the line of the joint therebetween disposed in a substantially horizontal position to join opposite side portions of said shell by an end wall in which the marginal portion of the latter which comprises the flange constitutes an integrally connected continuation of the side portions of the shell, and a stay element extending between and connected at its opposite ends to said shell and said closure respectively at positions adjacent said system of welding and spanning the latter, whereby the weld constitutes locally the sole means for relatively securing the marginal edge portions of said closure member and said shell and is protected by the flange against radially directed operating pressure forces, and against bending moments therein by said stay element.

8. The method of constructing a pressure vessel of the boiler type consisting in forming a casing portion with an inturned integral flange of substantial width at an end thereof, said flange being turned normal to the axis of said casing and adapted to adjoin the bordering edge of a closure member therefor, said closure member having marginal edge portions of uniform thickness and being applied to the opening defined by the marginal edge portions of said flange and joined directly thereto by a line of weld disposed peripherally of said closure and at a substantial distance inwardly from the line of said casing, and relatively bracing the marginal edge portions joined by said line of weld by means of stay elements connected at their opposite ends to said casing and to said closure member and spanning said line of weld.

- GEORGE M. TREF'IS, 3RD. 

